This just tells atspkg to look for a source file called
ats-src/ambitious-project.dats, which will be compiled to
ambitious-project.c in the default directory (i.e. cbits). You can then
call the generated code just as you would call C.

You may want to consider
ats-setup as well if you are
packaging the Haskell for distribution.

Calling Haskell from ATS

You can see a demo here.
Currently, there is not generic Storable instance that works with ATS, so the
process is a bit more involved than is ideal. atspkg has abilities similar to
hs2ats, which means that you can
usually generate ATS types based on the Haskell types.